i. Field of the invention
This invention relates to a novel interference screw made of bone and methods of use thereof in the field of orthopaedics.
ii. Background Art
Adequate fixation of graft material is one of the more important factors in successful outcome of cruciate ligament reconstruction. Numerous methods of graft fixation have been employed, including screw and washer, staples, buttons, and interference screws. Potential problems with residual hardware include chronic pain, migration, and loss of bone stock.
A number of interference screws are known in the art for use in fixation of cervical grafts (Zou et al, 1991) anterior cruciate ligaments (Matthews et al., 1989; Barrett et al., 1995; Kousa et a., 1995; Lemos et al., 1995; Kohn et al., 1994; Firer, P, 1991). In all of these studies, metallic or synthetic interference screws were utilized. Several such screws have been patented. Thus, for example, U.S. Pat. Nos. 5,470,334 (bioabsorbable synthetic interference bone fixation screw); 5,364,400 (synthetic biocompatible interference implant); 5,360,448 (porous-coated bone screw for securing prosthesis); 5,282,802 (use of an interference fixation screw made of a material that is soft compared to bone), describe various interference screws. As pointed out in several of these documents, metallic interference screws have the disadvantage of being made from a foreign substance which is not bioabsorbed and which therefore has the potential of long-term irritation and other complications. The synthetic interference screws likewise have a number of problems, even though allegedly being bioabsorbable. For example, there are difficulties in obtaining materials with sufficient rigidity and strength that are bioabsorbable. In addition, since the known synthetic bioabsorbable interference screws are not made of bone, they do not contribute to bone mass once they are bioabsorbed. None of these documents disclose an interference screw which itself is made from cortical bone.
Dr. J. M. Otero Vich published an article in 1985 relating to an "Anterior cervical interbody fusion with threaded cylindrical bone", (Vich, J. M., 1985), in which a modified Cloward dowel made from autologous or heterologous bone is described. Whereas the standard Cloward type dowel for cervical interbody fusion is a cylindrical dowel of bone taken from the iliac crest, Dr. Vich disclosed a technique in which there is required "the intraoperative threading of the cylindrical bone graft (either autologous or heterologous) to be implanted into the appropriate intervertebral space". Screw threads were placed in the graft with a small, previously sterilized die, and the graft was then screwed into a cylindrical bed in the intervertebral body. The entire disclosure is directed to production and use of a threaded intervertebral fusion implant. That implant, furthermore, is a bicortical dowel having an intermediate region composed of soft, porous cancellous bone, wholly inappropriate and too weak for use in the instant invention. The differences between cortical bone and cancellous bone implant healing are reviewed by Burchardt (Burchardt, 1983). There is no disclosure or suggestion of an interference screw made entirely of cortical bone.
Accordingly, there is a need in the art for a stable, strong interference screw made from cortical bone. This disclosure provides such a device, as well as methods for utilizing such a device.